The situation of living and operating in a free nation in which covert activities may invade upon personal privacy and, at the same time, a hostile national environment during high terror risk or wartime conditions creates an environment where, for example, vehicles become an available target for espionage and surveillance activists, for terrorists and for insurgents to typically place magnetically affixed location finders and even bombs to motor vehicle undercarriages, bumpers, wheel wells and quarter panels. Due to their affinity to strong magnetic adherence to these metal parts, the bomb devices are called “sticky IEDs.” The location trackers with associated Global Positioning System radio frequency broadcast are called “sticky location finders.” Also, containers are often used with magnets to permit the containers to be concealed under the vehicle body or in wheel wells. For example, small containers with affixed permanent magnets are used to contain a vehicle ignition/lock key so that a driver, not having the key and the vehicle being locked, may, knowing the location of the container, obtain the key and drive the vehicle. Other containers using magnets may be used to contain illegal drugs, contraband, valuable documents, money and the like. Such a device may be referred to herein as a “sticky container.” Other “sticky” devices may come to mind to one of ordinary skill in the art.
Sticky devices have been known to exist since at least the year 2000 and their use has been increasing. Rigged with magnets so that they will adhere to the undersides of automobiles and armored vehicles, sticky IEDs are often detonated by remote control or with timers. Consequently, sticky IED's (and also sticky location finders) may be covertly placed at one point in time, and activated once the car is moved. The sticky IED's then may be guaranteed to have at least one victim operating the vehicle. According to sources quoted on Dec. 3, 2010 via National Public Radio, currently 100 IED's are detonated each month in Iraq. The number previously was at 50 per month. In the month of November, 2010, the number of sticky IED's was 45. According to Ahmed Mawla, an explosives disposal instructor in Iraq, during the most painful times in Iraq, the number of IED's detonated reached fifty per day. Also, as of December, 2010, National Public Radio alleges that as many as 2196 deaths of US service members are attributable to IED's.
The sticky location finder is activated and can continuously monitor and broadcast vehicle location data as the vehicle moves in real time via radio frequency channels. Other initiation devices consist of movement detection mechanisms that activate the GPS unit (to save battery) or to destroy the targeted vehicle when it is started and then moved. Magnetic components of sticky IED's, sticky location finders and sticky containers may consist of imported components including, more importantly variable magnetic field characteristics and alloy compositions, for example, ceramic magnets versus AlNiCo versus SmCo versus NdFe or other permanent magnets of different alloy compositions and percentage weights.
Sticky containers may be used by rental car companies to hide keys to vehicles left on city streets for use by drivers needing vehicles that are available for rent by the hour or day. A car owner may use a sticky container to hide a key so that a co-owner, knowing the location may find the key and use it. At times, such intended placement of a magnetic container at a particular location may become unknown just as it may be the intention to use a sticky container to intentionally hide, for example, illegal drugs. Consequently, there may be a need for a magnetic field sensor for detecting such sticky containers.
The responsibility for detecting/knowing location of these sticky devices typically rests, first, with the vehicle driver or owner. When vehicles enter compounds, security personnel typically use mirrors to examine undercarriages and other metal portions of motor vehicles. Referring to FIG. 1A, there is shown a drawing of a mirror detector 100 held by a user 160. The detector may comprise in combination a flashlight 115 for shining on a mirror 110 in order to illuminate an undercarriage of a vehicle 150. Detector 100 typically is formed as a pole mirror mount and handle 120 so that user 160 may twist and maneuver the mirror to visually identify any unusual devices that may be affixed to the undercarriage. In order to view above a vehicle and with reference to FIG. 1B, a detector 110 may have a mirror 110 carried across a top of a vehicle as the vehicle drives through a security check point by a pole mount and handle 120. These methods of vehicle examination are not infallible since they rely on human discretion to look for, identify, and remove these devices. Most of these sticky devices are camouflaged so as to not be easily seen, for example, by using black surface paint, tar, undercoating and other materials so as to blend in with the car surface. Consequently, mirrors 110 are not perfectly effective.
Carl V. Nelson et al. for Johns Hopkins University has performed research in the field of detecting an identifying metal targets. U.S. Pat. No. 6,853,194 describes an electromagnetic target discriminator sensor system and method for detecting and identifying metal targets. A prior art system describe by FIG. 1 suggests a pulse transmitter and receiver coil for determining the existence of a metal target by inducing an eddy current in the target. Such a system has an obvious disadvantage in that, by inducing a current (or voltage), a user of the depicted detector may trigger a target device to actuate and have disastrous consequences for the user of the equipment. Nevertheless, Nelson persists in utilizing a wireloop transmitter and a wireloop receiver for, for example, detecting a buried metal target bomb in his '184 patent disclosure and drawings. U.S. Pat. No. 7,227,466 describes the use of an expendable metal detector that may be in the form of a hand-thrown or guided missile that may be launched toward an improvised explosive device (IED). Once the device lands, the tip may be buried next to the IED and magnetometers actuated. The missile tip may contain an impact switch for activating first and second magnetometers spaced from one another in the missile. In this manner, the magnetic fields detected by the magnetometers may be differentiated at a difference amplifier and the result transmitted by telemetry to a decision station. Clearly, the use of a missile with differential analysis may help to locate the sticky device while preserving the safety of deploying personnel.
In the field of automobile detection and identification, it is known to obtain and compare am induction signature of a motor vehicle with a stored induction signature and so identify the motor vehicle from U.S. Pat. Nos. 6,342,845 of Hilliard et al. and 7,771,064 of Leibowitz et al. A plurality of successive induction measurements or an induction signature for a given vehicle passively captured as the vehicle passes over a blade sensor in a lane of a road may classify the vehicle (for example, as a truck or car) and even identify the vehicle. Typically, the entire vehicle passes over the blade sensor which may be buried in a road surface. As the vehicle passes over the blade sensor, the signature is captured over the time it takes for the vehicle to pass over the blade sensor.
In the field of automotive vehicle maintenance (including flying vehicles such as helicopters), it is known from U.S. Pat. No. 4,100,491 to provide a soft iron core pole piece which may be magnetized by a magnetic field. The magnetized soft iron core causes engine oil particles of the engine to adhere to the polarized magnet. As engine particles accumulate on a probe portion for mounting in an engine oil flow line, an electronic control circuit identifies the accumulation of engine particles in oil (dirty oil) and provides a green (clean oil), yellow (oil caution) and red (dirty oil) indication to a driver or one responsible for engine maintenance. A feature of the circuit is the application of a brief alternating current to the soft iron core to remove residual magnetism (make the indicator green again), for example, after the engine oil is changed.
Furthermore, besides magnetometers and soft iron core detection circuits, Hall-effect sensors are known for use, for example, in determining the angular velocity of engines by detecting a magnetic field with each turn of an engine shaft. Edward Ramson, in his book, Hall-Effect Sensors, Elssevier, 2006, provides a thorough explanation of the use of Hall-effect sensors. Ramsom includes chapters providing exemplary linear Hall-effect sensor circuits for, for example, head-on sensing of magnets. However, Ramson explains that Hall-effect sensors are notoriously variable in terms of their magnetic field detection characteristics. A typical remnant induction or flux density B present in a closed ring in a saturated state for a typical ceramic magnetic may be 3850 gauss. For an AlNiCo magnet, a range in B may be from 8200 to 12,800 gauss and for NdFeB up to 13,500 gauss. Hall-effect sensors are on/off binary devices operative at a relatively high sensor on point and to turn off at a relatively low level of gauss. Magnetic field strength diminishes with the square of the distance. So the closer any magnetic field detector is to a magnet, the more likely the detector will turn on. Temperature also impacts both the residual level of gauss in a permanent magnet and also impacts the characteristics of the field detector.
Other devices are known such as chromatic cameras for detecting small differences in color variation, Moreover, radio frequency transmission detectors (typically involving wide band antennae covering a large range of frequencies may be utilized to detect radio frequency transmission from either a location finder device or emanating from a poorly shielded radio frequency receiver used to detonate a sticky IED.
In view of the above, there is clearly a need in the art for improved systems and methods for detecting the presence of sticky devices, for example, of the GPS or IED type so that they may be safely deactivated and removed from the vehicles on which they are found.